Text-to-speech conversion is a complex process whereby a stream of written text is converted into an audio output file. There are many known text-to-speech programs which convert text to audio. A conversion algorithm, in order to convert text-to-speech, has to understand the composition of the text that is to be converted. One known way in which text composition is performed is to split the text into what is known as phonemes. A phoneme can be thought of as the smallest unit of speech that distinguishes the meaning of a word. However, one disadvantage with this approach is that by breaking the text into phonemes the quality of the output speech is decreased because of the complexity of combining the phonemes once again to form the synthetic speech audio output file.
Another known method is to split phrases within a line of text not at the transition of one phrase to another but at the center of the phonemes, which leaves the transition intact (diphone method). This method results in better quality synthetic speech output but the resulting audio file uses more disk storage space.
Another form of text-to-speech conversion algorithm creates speech by generating sounds through a digitized speech method. The resulting output is not as natural sounding as the phoneme or diphones algorithms, but does have the advantage of requiring less storage space for the resulting converted speech.
Thus, there is a trade-off to be made between having a speech output which is very natural sounding and requiring a large amount of computation power and computer storage space and speech output which sounds computer generated and which does not require a large amount of computational power and a large amount of storage space.
Whichever type of text-to-speech algorithm is used for the conversion it is always difficult to determine how much storage space is required. This problem is compounded when the storage device is a portable storage device such as a USB device as it is difficult to predict how much of the converted data will fit onto the storage device.
A further complication arises when files of different types are converted. This is because different file types comprise different characteristics and properties which affect the resulting size of the file. For example, a paragraph of text comprises 38 words and 210 characters and can be written to a ‘.txt’ file and a ‘.doc’ file. The file size of the ‘.txt’ file is 4.0 KB and the file size of the ‘.doc’ file is 20 KB.
Thus it would be desirable to alleviate these and other problems associated with the related art.